A yeast extract is an extract obtained by extracting useful components of yeast. The yeast extract contains amino acids, nucleic acid-related substances, minerals, and vitamins as the main component, and is used in various fields of pharmaceuticals, culture media, foods, feeds, and the like. In particular, in a food production process, a yeast extract is used for improving or enhancing a flavor. Demand for the yeast extract has been increased for its good image of being a natural material, and the production quantity has been increasing year by year.
Various methods such as autolysis method, hydrothermal treatment method, and enzymatic treatment method are used for producing a yeast extract. A yeast autolysate is obtained by autolyzing the cells with digestive enzymes contained in the yeast cells. In this way, proteins constituting yeast are decomposed into amino acids or low-molecular peptide chains having umami taste.
When a yeast extract is produced by such an autolysis method, it is desired to increase the content of the useful components in the extract.
For example, in a production process of a yeast extract, autolysis can be promoted by adding toluene, ethyl acetate, an inorganic acid, or the like. In addition, a method of promoting autolysis is as follows.
For example, in Japanese Patent Application Laid-Open Publication No. H10-179084 (Patent Document 1), disclosed is a technique in which, in producing a yeast extract by the autolysis method, the first stage of enzyme reaction is performed at the optimal reaction temperature at which an enzyme among the proteases contained in yeast is more actively reacted in a low temperature range, subsequently, the second stage of enzyme reaction is performed at a temperature higher than the optimal reaction temperature and in the temperature range in which propagation of bacteria is suppressed, or higher, and further the third stage or more of enzyme reactions with different enzyme reaction temperatures are performed.
In addition, in Japanese Patent No. 5730579 (Patent Document 2), disclosed is a method of producing yeast highly containing amino acids in which yeast in the stationary phase of growth is cultured under the condition that the pH of the liquid medium is 7.5 or more and less than 11. In this way, yeast highly containing amino acids can be obtained.